The present invention relates generally to radiation therapy, and more particularly, to a method and system for reconstructing an intensity map from segments defining an intensity modulation radiation treatment.
Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of patients. A radiation therapy device generally includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located within the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam may be an electron beam or photon (x-ray) beam, for example. During treatment, the radiation beam is trained on a zone of a patient lying in the isocenter of the gantry rotation.
In order to control the radiation emitted toward the patient, a beam shielding device, such as a plate arrangement or collimator, is typically provided in the trajectory of the radiation beam between the radiation source and the patient. An example of a plate arrangement is a set of four plates which can be used to define an opening for the radiation beam. The collimator is a beam shielding device which may include multiple leaves (e.g., relatively thin plates or rods) typically arranged as opposing leaf pairs. The plates are formed of a relatively dense and radiation impervious material and are generally independently positionable to delimit the radiation beam.
The beam shielding device defines a field on the zone of the patient for which a prescribed amount of radiation is to be delivered. The usual treatment field shape results in a three-dimensional treatment volume which includes segments of normal tissue, thereby limiting the dose that can be given to the tumor. The dose delivered to the tumor can be increased if the amount of normal tissue being irradiated is decreased and the dose delivered to the normal tissue is decreased. Avoidance of delivery of radiation to the healthy organs surrounding and overlying the tumor limits the dosage that can be delivered to the tumor.
The delivery of radiation by a radiation therapy device is typically prescribed by an oncologist. The prescription is a definition of a particular volume and level of radiation permitted to be delivered to that volume. Actual operation of the radiation equipment, however, is normally done by a therapist. The radiation emitting device is programmed to deliver the specific treatment prescribed by the oncologist. When programming the device for treatment, the therapist has to take into account the actual radiation output and has to adjust the dose delivery based on the plate arrangement opening to achieve the prescribed radiation treatment at the desired depth in the target.
The radiation therapist""s challenge is to determine the best number of fields and intensity levels to optimize dose volume histograms, which define a cumulative level of radiation that is to be delivered to a specified volume. Typical optimization engines optimize the dose volume histograms by considering the oncologist""s prescription, or three-dimensional specification of the dosage to be delivered. In such optimization engines, the three-dimensional volume is broken into cells, each cell defining a particular level of radiation to be administered. The outputs of the optimization engines are intensity maps, which are determined by varying the intensity at each cell in the map. The intensity maps specify a number of fields defining optimized intensity levels at each cell. The fields may be statically or dynamically modulated, such that a different accumulated dosage is received at different points in the field. Once radiation has been delivered according to the intensity map, the accumulated dosage at each cell, or dose volume histogram, should correspond to the prescription as closely as possible.
Many conventional treatment planning systems do not export intensity maps, but instead export only segments defining an intensity modulated radiation treatment. However, software used with radiation therapy equipment often requires an intensity map. The systems may calculate intensity maps from their internally generated segments, however, this is done only for comparison with the original intensity map in order to perform fluence correction to minimize the difference between the original intended map and the actual deliverable map. These systems are not designed to create an importable intensity map from an external source of segments. Furthermore, conventional systems can not communicate with other planning systems that only produce segments for the purpose of creating intensity maps and creating a more efficient set of segments. These systems may import segments, but only for the purpose of doing a direct dose distribution calculation, and not for the purpose of creating a new intensity map that can be used to create new segments. Conventional treatment planning systems that do not export intensity maps are not able to take advantage of the segmentation capabilities of software such as IMFAST (available from Siemens Corporation), since this software performs segmentation starting from intensity maps.
Accordingly, there is therefore, a need for a system and method that reconstructs intensity maps from imported segments to allow for the exchange of intensity maps indirectly by exchanging segments.
A method and system for reconstructing an intensity map from segments are disclosed.
A method for reconstructing an intensity map generally comprises importing a set of segments and analyzing the segments to determine intensity map geometry. Radiation contributions are calculated for each cell in each of the segments and a reconstructed intensity map is created.
A system for reconstructing an intensity map generally comprises a processor configured to import a set of segments from a treatment planning system and operable to analyze the segments to determine intensity map geometry, calculate radiation contributions for each cell in each of the segments, and create a reconstructed intensity map. The system further includes memory operable to at least temporarily store the segments.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.